feat(babel‑types): Add type definitions for Node assertion methods

[ExE-Boss]

Q	A
Fixed Issues?
Patch: Bug Fix?	Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	No
License	MIT

This adds TypeScript and Flow type definitions for the assert${typeName} functions.

It also makes use of the typesVersions field, which was introduced in TypeScript 3.1 to make the assert${typeName} functions into assertion functions without breaking backwards compatibility, like what I did with @types/babel‑types in DefinitelyTyped/DefinitelyTyped#45830.

This also now generates /** @deprecated */ JSDoc comments for deprecated node type checking functions.

---

review?(@JLHwung, @MichaReiser, @nicolo-ribaudo)

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[ExE-Boss]

/ping @JLHwung

[JLHwung]

nit: I think we can swap the name of ts37.d.ts with index.d.ts. So index.d.ts always align to latest TS, and we can have lib/legacy.d.ts as fallback.

{
  "types": "lib/legacy.d.ts",
  "typesVersions": {
    ">=3.7": {
      "*": "lib/index.d.ts"
    }
}

[ExE-Boss]

The thing is, importing lib/index.js directly would cause old TypeScript versions to try to load lib/index.d.ts, but that would then have the TypeScript 3.7 syntax.

Using index.ts37.d.ts also ensures that we can easily add index.tsXY.d.ts (e.g.: index.ts40.d.ts) in the future.

[JLHwung]

We will disable submodule imports in Babel 8. And we could drop ts <3.0 support, too. So tsc will always respect typeVersions and types and we can enforce that lib/index.d.ts always aligns to latest TS while typeVersions serves a fallback for older ts>=3 versions.

[ExE-Boss]

typesVersions is only supported since TypeScript 3.1.

---

Also, this will need to be kept as index.ts37.d.ts in Babel 7.

[nicolo-ribaudo]

I didn't notice this PR and did a9bc9be yesterday. However, this PR still added some improvements (assert* definitions for older TS versions, and @deprecated annotations) so I have rebased it.

Thanks! 😄